The present invention relates to a thick-film bubble detector having both a function of propagating magnetic bubbles and a function of detecting them.
A magnetic bubble device is required to have a bubble detector for detecting the presence or absence of a magnetic bubble in the form of an electric signal. In a magnetic bubble device using magnetic bubble propagation elements made of a soft magnetic material such as permalloy (namely, a nickel-iron alloy), a single soft-magnetic layer can be used to propagate magnetic bubbles and to detect them, that is, the so-called thick-film bubble detector can be used. This detector is formed of the soft-magnetic layer having a chevron pattern or modified chevron pattern. Further, in a detection part of the detector, a plurality of bubble propagation elements each having the form of a chevron are electrically connected in series, and supplied with a constant current. When a magnetic bubble is propagated to the detector, it is first elongated (or stretched) in lateral directions perpendicular to a bubble propagation direction. When the magnetic bubble thus stretched passes through the detection part of the detector, the soft magnetic material forming the detection part is changed in the state of magnetization, and therefore the electric resistance of the above soft magnetic material is varied on the basis of the magnetoresistance effect. The resistance change at the detection part is detected in the form of a voltage change, since the constant current flows through the detection part. Thus, the magnetic bubble can be detected by the detection part. The magnetic bubble thus detected is sent to the outside of an effective region of the device, to be erased. Accordingly, the bubble detector is divided into three main parts, that is, a stretcher part for stretching a magnetic bubble, a detection part for electrically detecting the magnetic bubble, and a send-out part for sending out the magnetic bubble to the outside of an effective region. In order to gradually stretch the magnetic bubble, the stretcher part has the form of a triangle (or sector), that is, the width of the stretcher part is smallest at the entrance thereof, and increases as the distance from the entrance becomes larger.
In conventional bubble detectors, the stretcher, detection and send-out parts are made equal to each other in the period of arrangement of bubble propagation elements forming each part viewed in a bubble propagation direction (hereinafter simply referred to as "the period of the bubble propagation element"), or the stretcher part is made equal to the send-out part but different from the detection part in the period of the bubble propagation element. In either case, the period of the bubble propagation element is kept constant in the stretcher part.
In the case where magnetic bubbles having a small diameter are used, the period of the bubble propagation element at the stretcher part is usually made larger than the period of the arrangement of fundamental bubble propagation elements forming a minor loop or others viewed in a bubble propagation direction, to generate a strong magnetic pole at the stretcher part by making large the period of the bubble propagation element at the stretcher part, thereby enhancing the bubble stretching capacity of the stretcher part. Further, it is also desirable from another point of view to make large the period of the propagation element at the stretcher. That is, the detection part judges the presence or absence of the magnetic bubble on the basis of leakage flux from magnetic bubbles, and therefore a detection signal outputted from the detection part is affected not only by the leakage flux from a magnetic bubble to be detected, but also by the leakage flux from magnetic bubbles proximate to the to-be-detected magnetic bubble. Accordingly, the detection signal varies with the distribution of magnetic bubbles (that is, the state of data) in the vicinity of the detection part. This makes it difficult to judge the presence or absence of magnetic bubble. The influence of the magnetic bubbles proximate to the to-be-detected magnetic bubble on the detection signal can be reduced by making large the distance between adjacent magnetic bubbles in the bubble propagation direction, that is, the period of the bubble propagation element. For these reasons, the period of the propagation element has hitherto been made large everywhere at the stretcher part.
As mentioned above, in order to enhance the margin of stretching bubbles at the stretcher part and to reduce the influence of magnetic bubbles proximate to a to-be-detected magnetic bubble on the detector part, it is desirable to make the period of the propagation element large at the stretcher part. However, in the case where the period of the propagation element is made large at the entrance portion (namely, sector portion) of the stretcher part, a malfunction that a stretching magnetic bubble is not propagated partly, is performed when a bias magnetic field is low, and therefore the bubble propagation margin of the stretcher part is reduced, that is, the range of bias magnetic field in which a magnetic bubble is normally propagated, is narrowed.